Some of mankind's greatest medical threats are caused by viruses, including AIDS, hepatitis, rhinovirus infections of the respiratory tract, flu, measles, polio and others. There are a number of chronic persistent diseases caused by RNA or DNA viruses, that replicate through a RNA intermediate, which are difficult to treat, such as hepatitis B and C, and HIV. A number of common human diseases are caused by RNA viruses that are replicated by a viral encoded RNA replicase. Included in this group are influenza (Zurcher, et al., J. Gen. Virol. 77:1745 (1996)), dengue fever (Becker, Virus-Genes 9:33 (1994)), and rhinovirus infections (Horsnell, et al., J. Gen. Virol., 76:2549 (1995)). Animals also suffer from a wide variety of RNA viral diseases, including feline leukemia and immunodeficiency, Visna maedi of sheep, bovine viral diarrhea, bovine mucosal disease, and bovine leukemia. Although some vaccines are available for DNA viruses, diseases such as hepatitis B are still prevalent. Hepatitis B is caused by a DNA virus that replicates its genome through a RNA intermediate (Summers and Mason, Cell 29:4003 (1982)). While an effective vaccine exists as a preventive, treatment for chronic persistent Hepatitis B Viral (HBV) infection only cures a minority of patients.
Chain terminating nucleoside analogs have been used extensively for the treatment of infections by DNA viruses and retroviruses. These analogs have been designed to be incorporated into DNA by DNA polymerases or reverse transcriptases. Once incorporated, they cannot be further extended and thus terminate DNA synthesis. Unfortunately, there is immediate selective pressure for the development of resistance against such chain terminating analogs that results in development of mutations in the viral polymerase that prevent incorporation of the nucleoside analog.
An alternative strategy is to utilize mutagenic deoxyribonucleosides (MDRN) or mutagenic ribonucleosides (MRN) that are preferentially incorporated into a viral genome. MDRN are incorporated into DNA by viral reverse transcriptase or by a DNA polymerase enzyme. MRN are incorporated into viral RNAs by viral RNA replicases. As a result, the mutations in the viral genome affect all viral proteins by creating inactive versions of them. These mutations are perpetuated and accumulated with each viral replication cycle. Eventually, through the sheer number of mutations, a gene which is necessary for the function, replication, or transfection of the virus will be inactivated which will cease the viral life cycle. Because MDRN and MRN are not specifically targeting one particular viral protein, there is less likelihood for the development of resistance.
5-aza-2′-deoxycytidine (5-aza-dC) is an antineoplastic agent that has been tested in patients with leukemia and is thought to act predominantly by demethylating DNA. Methylation is thought to silence tumor growth suppressor and differentiation genes. Interestingly, 5-aza-dC affects other targets. For example, 5-aza-dC was shown to inhibit HIV replication in vitro, although the mechanism of action was not determined (see e.g., Bouchard et al, Antimicrob. Agents Chemother. 34:206–209 (2000)). Deamination of 5-aza-dC to 5-aza-2′-deoxyuridine (5-aza-dU) has been shown to result in loss of antineoplastic activity (see e.g., Momparler, et al., Leukemia. 11:1–6 (1997)).
While 5-azacytidine (5-aza-C) or 5-aza-dC and variants thereof show promise as MDRNs and MRNs, these compounds are also unstable and rapidly degrade upon reconstitution. For example, at pH 7.0, a 10% degradation in 5-aza-dC occurs at temperatures of 25° C. and 50° C. after 5 and 0.5 hours, respectively (see e.g., Van Groeningen et al., Cancer Res. 46:4831–4836 (1986)). Thus, therapeutic use of these compounds is limited for treatment of both viral diseases and cancer. The present invention solves this and other problems.